1. Field of the Invention
The present invention relates to a plasma display panel (PDP), and more particularly, to a discharge electrode and a phosphor for a PDP, which displays a color image.
2. Background of the Related Art
Generally, a PDP and a liquid crystal display (LCD) have lately attracted considerable attention as the most practical next display of panel displays. In particular, the PDP has higher luminance and wider visible angle than the LCD. For this reason, the PDP is widely used as a thin type large display such as an outdoor advertising tower, a wall TV, and a theater display.
The PDP performs display operation in such a manner to emit a phosphor using ultraviolet rays generated by gas discharge. Such a PDP includes an AC PDP having a dielectric layer on an electrode surface and a DC PDP in which an electrode surface is exposed to a discharge space. In the AC PDP, the phosphor is formed on the dielectric layer. In the DC PDP, the phosphor is formed on the electrode.
FIG. 1 shows a structure of a related art AC PDP of three-electrode area discharge type. As shown in FIG. 1, the related art AC PDP of three-electrode area discharge type includes an upper structure, a lower structure, and a discharge area 5. The upper structure includes an upper electrode 4 having a Y electrode and a Z electrode on the same plane of a front glass substrate 1, a dielectric layer 2 formed on the upper electrode 4 by printing, and a passivation layer formed on the dielectric layer 2. The lower structure includes an X electrode 12 formed on a rear glass substrate 11 of the upper structure to cross the upper electrode 4, an isolation wall 6 formed between the X electrode and the X electrode to prevent crosstalk between adjacent cells, and phosphors 8, 9 and 10 formed around the isolation wall 6 and the X electrode 12. The discharge area 5 is formed by sealing an inert gas in a space between the upper structure and the lower structure. For reference, in FIG. 1, the upper substrate is rotated by 90xc2x0.
The AC PDP of three-electrode area discharge type generates opposite discharge between the X electrode and the Y electrode if a driving voltage is applied between the X electrode and the Y electrode. As a result, wall charge occurs on a surface of the passivation layer of the upper structure. If discharge voltages having opposite polarities are continuously applied to the Y electrode and the Z electrode while the driving voltage applied to the X electrode is broken, area discharge occurs in the discharge area on surfaces of the passivation layer 3 and the dielectric layer 2 due to potential difference which is generated between the Y electrode and the Z electrode by wall charge. This area discharge generates ultraviolet rays 7 from the inert gas of the discharge area. The ultraviolet rays 7 excite the phosphors 8, 9, and 10. The excited phosphors 8, 9 and 10 are emitted to display color.
In other words, electrons in the discharge cell are accelerated to negative electrode by the driving voltage. The accelerated electrons come into collision with the inert mixing gas filled in the discharge cell at a pressure of 400xcx9c600 torr. The inert mixing gas is a penning mixing gas containing He as a main component and further containing Xe and Ne. The inert gas is excited by the collision to generate ultraviolet rays having a wavelength of 147 nm. The ultraviolet rays come into collision with the phosphors 8, 9 and 10 surrounding the lower electrode 12 and the isolation wall 6, so that light of a visible right ray region is emitted.
The PDP discharges a cell having pixels by controlling the voltages applied to the X, Y and Z electrodes. The intensity of light emitted by this discharge varies discharge time of the cell. In other words, gray scale required to display and image displays the image within the time required to display the entire image, for example, 1/30 seconds in case of NTSC TV signal, by varying the time length of discharge for each cell. At this time, the luminance of the screen is determined by brightness when each cell is discharged to the utmost. To obtain the highest luminance in the PDP screen, it is necessary to maintain the discharge time of the cell to the utmost within the time required to display one screen.
FIG. 2 is a block diagram showing a structure of a PDP having a driving circuit, in which a panel, an X electrode drive 10, a Y electrode driver 20 and a Z electrode driver 30 are shown.
The X electrode 12 formed in each cell of the PDP in FIG. 1 is connected to the X electrode driver 10 so that an address voltage is applied to the X electrode 12. The Y electrode 25 is connected to the Y electrode driver 20 so that a scan voltage is applied to the Y electrode 25. The Z electrode 35 is connected to the Z electrode driver 30 so that a sustain voltage is applied to the Z electrode 35.
The X, Y and Z electrodes constitute a matrix arrangement. The matrix arrangement acts as a display area 50 of the PDP. The Y electrode 25 and the Z electrode 35 in FIG. 2 correspond to the upper electrode 4 in FIG. 1.
FIG. 3 shows waveforms of pulses applied to the respective electrodes of the PDP, in which the respective pulses show different waveforms in a reset period, an address period and a sustain period.
A reset pulse 21 of the scan voltage output from the Y electrode driver 20 is simultaneously applied to all of Y electrodes 25 in each discharge cell of the PDP. The Y electrode driver 20 inserts a scan pulse 22 into a sustain pulse 80 of the scan voltage applied to the Y electrode 25 so as to generate opposite discharge against the X electrode 20 referring to scan data. At this time, an address pulse 60 output from the X electrode driver 10 is applied to the X electrode 12. The sustain voltage applied to the Z electrode 35 has a phase opposite to the sustain pulse 80 of the scan voltage and has the same period as the sustain pulse. The address pulse 60 applied to the X electrode 12 is synchronized with the scan pulse 22 applied to the Y electrode 25 and has a phase opposite to the scan pulse. Accordingly, the X electrode 12 and the Y electrode 25 generate opposite discharge by voltage difference between the address pulse 60 and the scan pulse 22. The Y electrode 25 and the Z electrode 35 generate area discharge by voltage difference between the sustain pulse of the scan voltage and the sustain voltage. Then, if the address pulse 60 is applied to the scan voltage, area discharge stops, thereby turning off the discharge cell.
In case of opposite discharge, a red phosphor, a blue phosphor and a green phosphor formed in each discharge cell are emitted by different voltage levels, respectively. In other words, a discharge voltage in which ultraviolet rays for emitting the red phosphor are generated, a discharge voltage in which ultraviolet rays for emitting the blue phosphor are generated, and a discharge voltage in which ultraviolet rays for emitting the green phosphor are generated differ from one another because dielectric constants of the respective phosphors differ from one another. Therefore, the opposite discharge time and luminance are varied depending on the respective phosphors formed in the discharge cells of the PDP even if the same discharge voltage is applied to the respective discharge cells.
FIG. 4 shows an equivalent circuit of discharge cells of the PDP to which the discharge voltage is applied.
It is assumed that the phosphors are deposited on the electrode of the upper substrate in the same manner as the related art three-electrode area discharge type.
In FIG. 4, a voltage Vs is an externally applied voltage to the discharge cell, C1 is a capacitance of the upper substrate in the cell to be discharged, Cg is a capacitance of the discharge space, Cp is a capacitance of the phosphor to be emitted, and C2 is a capacitance of the lower substrate in the cell to be discharged excluding Cp.
The voltage applied to the discharge space of the respective discharge cells is susceptible to the capacitance of the phosphors formed in the respective discharge cells. The capacitance of the phosphors is determined by the thickness of the phosphors and their dielectric constants. Generally, the dielectric constant of the green phosphor is greater than the dielectric constants of the red and blue phosphors. Therefore, the voltage applied to the discharge area of the discharge cell of the green phosphor is smaller than the voltages applied to the discharge areas of the discharge cells of the red and blue phosphors.
The aforementioned related art PDP has several problems.
Since the voltage applied to the discharge space of the respective cells is susceptible to the capacitance of the phosphors formed in the respective discharge cells, the discharge voltage actually applied to the discharge area is varied depending on the respective discharge cells, thereby generating differences in emitting luminance and emitting time.
In other words, the capacitance of the capacitor of the phosphors is determined by the thickness and dielectric constants of the respective phosphors. Since the dielectric constant of the green phosphor is greater than the dielectric constants of the green and blue phosphors, the voltage applied to the discharge area of the discharge cell of the green phosphor is smaller than the voltages applied to the discharge areas of the discharge cells of the green and blue phosphors. Accordingly, if the same voltage is applied to the respective discharge cells, the discharge cell of the green phosphor is emitted for the last time, thereby deteriorating picture quality of the PDP.
Accordingly, the present invention is directed to a PDP that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a PDP in which the same discharge voltage is maintained in all of discharge cells.
Other object of the present invention is to provide a PDP which minimizes a capacitance of phosphors by removing some of the phosphors of each discharge cell to maintain almost same discharge voltage level applied to discharge areas of each discharge cell.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a PDP according to the present invention includes a plurality of lower electrodes successively formed on a first substrate in row direction, a plurality of isolation walls formed between the lower electrodes, a plurality of upper electrode sets successively formed on a second substrate opposite to the first substrate to cross the lower electrodes, and a phosphor formed on the first substrate to expose some of the lower electrodes crossed the upper electrode sets.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.